The present invention refers to a hub-bearing assembly fort a soil working disc, particularly a tilling disc.
These discs are usually arranged side to side on respective axles projecting from the frame of the plough or another similar agricultural machine. Each disc is rotatably mounted by means of a hub-bearing unit comprised of one or two stationary, radially inner races, fixed on a central axle projecting from an arm of the agricultural machine frame, a radially outer race which is integral with a radial outer flange for mounting the disc, and a dual set of balls interposed between the inner and outer races. The inner races, and therefore the whole bearing unit, are axially locked against a shoulder of the axle by tightening a ring nut screwed on the free outer end of the axle. See, for example, EP-B-1 326 489.
In order to prevent contaminants (water, mud, soil) from entering the bearing from the side opposite to that where the disc is mounted, i.e. on the side facing the arm of the frame, some bearing units have been equipped with sealing devices having sealing lips slidingly contacting interface shields. The sealing devices used heretofore have not proven to guarantee efficient sealing for long enough time, particularly if the locking nut is slightly unscrewed or loose.
Efficient sealing action is of primary importance for correct operation of the disc over an acceptable period of time. Since the contamination conditions are extreme, contaminants entering the inner parts of the bearing may rapidly lead to the locking of a disc, consequently reducing productivity. In some cases the entering of contaminants is due to the locking nut being partially unscrewed on the free end of the axle. Also, an efficient sealing action able to prevent leakage of lubricant out of the bearing is of primary importance for the protection of the environment, in order to prevent pollution of the soil by the lubricant.
The performance and life of sealing devices are also limited by metal wires that are used for tying up rolled bales and that are left on the field. These wires are inevitably picked up by the discs and tightly wound around the hubs, forming rather thick coils. The same wires, tangled around and beside the sealing device may destabilize it or move part of it so that the lips of the sealing device are no longer correctly positioned on the respective interface surfaces.